Tracking Tregs

The paper:

The finding:

Using a GFP-tagged knockin mouse, Alexander Rudensky's group at the University of Washington in Seattle showed that the expression of the transcription factor Foxp3 defines a subset of regulatory T cells involved in suppressing autoimmune activity.

The surprise:

Unlike most other transcription factors, which are expressed in multiple systems or tissues, Foxp3 was found only in a subset of αβ T cells. "It's a very rare instance when there is a dedicated function," Rudensky says. At the time, CD25 expression was the best available marker for identifying regulatory T cells; Foxp3's surprising specificity has since made it a more reliable marker.

The follow-up:

Rudensky and his colleagues found that Foxp3 expression not only defines regulatory T cells, but is also necessary for the suppressor function of these cells. This year Rudensky and several other groups published a list of Foxp3's genetic targets, which could help explain why the loss of the gene is catastrophic (see www.the-scientist.com/news/display/42904).

The work ahead:

Foxp3 expression could have additional functions, points out Fred Ramsdell of ZymoGenetics in Seattle. During T-cell activation there is a transient expression of Foxp3. "Some of those cells may go off to become regulatory T cells or some may not," Ramsdell says. "It's not clear and still needs to be worked out."